Generic object holders are, for instance, required in semiconductor technology. During the manufacture of semiconductor components, such as computer chips, wafers are coated several times and are chemically treated. In order to distribute reagents homogenously over the wafer or dry the wafer between two processing steps, the wafer is frequently rotated on its own axis. The wafer is frequently also rotated for quality control purposes when optical measuring methods are used. The holders which are employed must ensure that the wafer is also securely held during rotation, especially at high rotational speeds (normally 1200 rpm).
U.S. Pat. No. 6,167,893 B1, describes a dynamic chuck for semiconductor wafers. It comprises three clamping arms with supports for the wafer as well as pivotable grippers on the outside ends of the clamping arms. The pivotable grippers incorporate centrifugal weights. During the rotation of the chuck with the wafer, the centrifugal force pulls the centrifugal weights to the outside, causing the gripper fingers to pivot against the wafer edge and thus holding the wafer.
U.S. Pat. No. 6,363,623 B1 describes a device for rotating an object, e.g. a wafer. Work piece supports with resilient bumpers are symmetrically positioned on a rotatable platform. These resilient bumpers serve as support for the wafer and increase the friction between the wafer and the platform in order to reduce slippage, especially during the rotation. In addition, the device comprises gripper assemblies that are configured to center the wafer on the rotatable platform. The gripper assemblies are provided with pivotable fingers, which incorporate centrifugal weights, pivoting them against the wafer during rotation, due to the centrifugal force, thereby firmly securing it.
The wafer holding device described in U.S. Pat. No. 6,273,484 B1 also comprises a plurality of pivotable jaws with centrifugal weights. In addition, these jaws comprise a step portion for supporting the wafer during standstill. During rotation, the jaws pivot in such a manner that they hold down the wafer. When the wafer holding device comes to a stop after the rotation, the pivotable jaws are returned into their home position by means of springs.
The rotary processing apparatus for substrates described in U.S. Pat. No. 5,954,072 comprises pivotable grippers around the periphery of the plate-like substrate holder, which are pushed against the substrate, e.g. by means of springs, during standstill or at low rotation speeds. The additional pivoting action that results from the centrifugal forces during rotation holds down the substrate.
In the edge handling wafer, as described in U.S. Pat. No. 6,217,034, the wafer is carried along by spring-loaded clamping elements.
An air cushion between the wafer and the rotating table improves the axial runout of the clamped wafer, so that this device is also suitable for wafer inspection by optical measuring methods.
U.S. Pat. No. 5,775,000 describes a substrate gripper device for spin dryers comprising clamping arms with horizontal substrate supports with a plurality of pivotably mounted gripper fingers. Springs between the finger and the respective clamping arm ensure that the gripper fingers are pretensioned and hold the substrate on the substrate support. In order to open the holding device, the fingers are pivoted away from the substrate against the spring action by means of pins. In order to actuate the pins, a mechanism made up from an inner and an outer sleeve is provided, arranged around the rotational axis of the gripper. At the bottom end, the inner shaft is developed as a piston and the outer shaft as a cylinder. Both sleeves are moved against each other by means of a working fluid. During the movement of the two sleeves against each other, a cup-shaped element is moved in the direction of the opening pins. A cup shape with a rotatable substrate is necessary, because the entire mechanism does not rotate concurrently during the rotation of the clamping arms with the substrate. The pins, however, are attached to the clamping arm and also perform the rotation.
U.S. Pat. No. 6,537,416 B1 describes a wafer chuck with three centrally mounted clamping arms, which comprise support surfaces for the wafer and the connector pins. The connector pins also serve to align the wafer on the support surfaces, requiring the connector pins to be shifted in a radial direction. For this purpose, a pneumatic actuator is provided, which shifts a slide on the connector pin, which is pretensioned with a spring, from its holding position into the opening position. This opening mechanism is located outside of the clamping arms. This wafer chuck, can, for instance, not be positioned overhead, because the wafer would not be securely retained in all positions.
U.S. Pat. No. 2003/0110658 A1 describes a wafer holder comprising a circular body which comprises a multitude of spokes on its bottom side, each of which provide an actuating mechanism for the gripper finger arranged on the radial end. Since no support surface for the wafer is provided, the gripper fingers are designed so that they encompass the edge of the wafer. This holding device has the disadvantage in that the wafer must be fed from the top and be held in its position until the gripper fingers have grasped the wafer.